Ventricular assist device with valved blood conduit and method of making

ABSTRACT

A ventricular assist device includes a pair of valved conduits and a pumping portion connected by these conduits into the circulatory system of a host patient. The pumping portion and valved conduits are constructed and configured to minimize the number of material-surface transitions which blood must cross in flowing through the device. Also, the valved conduits include porcine xenograft valves, which are externally supported by stenting structure located outside of the blood-contacting flow path of the device. A flexible shape-retaining inner wall member of the valved conduits is impervious to blood, but defines a porous inner surface on which a stable biological interface may form. Also, this inner wall member is shaped with sinuses which do not replicate either the porcine sinuses from which the xenograft valves were taken, or human aortic sinuses. However, the sinuses of the inner wall member are configured to provide effective valve action by the formation of vigorous vortices in the blood flow downstream of these valves, and to avoid the formation of clots on the blood-contacting surfaces of the valved conduits.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is in the field of ventricular assistdevices, and of artificial prosthetic conduits used for transportingblood in the circulatory system of a living organism. More particularly,the present invention relates to a ventricular assist device whichincludes a continuous unitary blood-contacting membrane defining avariable-volume cavity, expansion and contraction of which is effectiveto pump blood; and to a valved blood conduit for communicating blood toor from the variable-volume chamber, and having liquid-impermeablemembrane or inner wall defining a blood-contacting surface within theconduit. The inner wall of the conduit sealingly engages the unitaryblood-contacting membrane of the variable-volume chamber without ablood-contacting gasket or sealing member, so that only a singlematerial-surface transition is experienced by the flowing blood uponentry into or outflow from the ventricular assist device.

[0003] Also, the present invention relates to an artificial conduithaving therein a prosthetic bio-material valve structure, and associatedconduit structure for ensuring a substantially laminar central jet ofblood flow through the conduit and valve structure, while also ensuringthat flow disruption is minimized, and that no blood stagnation orstasis volumes are formed downstream of or behind the valve structure.Still more particularly, the present invention relates to such a valvedblood conduit having woven and/or knitted filamentary fabric walls whichare impregnated outwardly with a biologically-compatible impermeablematerial so that the conduit walls are impermeable to blood, while theinner surface of the conduit wall remains textured or porous to promotethe growth of a stable biological interface. Provision is made forsealingly connecting the valved blood conduit to other blood-carryingcomponents without disruption of smooth and stasis-free blood flow. Theconnecting provisions also minimize the number of blood-contactingmaterial-surface transitions, and provide for accommodation without lossof sealing integrity of dimensional changes which will occur at theconnections after implantation of the valved conduit and assist device.These dimensional changes will occur as a transitional collagen or otherbiodegradable coating of the conduit is absorbed, as components of thevalved conduit and adjacent structure take a set with the passage oftime after surgical implantation, and as a biological interface isformed on the blood-contacting surfaces by the host's circulatorysystem.

[0004] 2. Related Technology

[0005] Ventricular assist devices have become increasingly recognized aspotentially able to allow patient's whose natural heart is diseased orhas been injured by trauma or heart attack, to recover and continuelife, either while their natural heart heals, while awaiting a hearttransplant, or even on a long-term basis with the extended aid of theventricular assist device.

[0006] Particularly, left-ventricular assist devices (LVAD) arerecognized as potentially very valuable for assisting patients whosuffer from congestive heart failure. More than two and one-half millionAmericans suffer from congestive heart failure. Recently, a NationalInstitutes of Health study estimated that as many as thirty-fivethousand people could be candidates for use of a left-ventricular assistdevice. At present, the conventional ventricular assist devices are usedfor patients who are waiting for a heart transplant (a so-called,“bridge to transplant”), for patients whose natural heart is of suchpoor condition that the patient cannot be removed from a heart-lungmachine without providing some assistance to the patient's heartfollowing otherwise successful open-heart surgery, and for patientssuffering from massive heart attacks that lead to circulatory collapse.The conventional left-ventricular assist devices are not generallyconsidered to be viable candidates for long-term utilization outside ofthe clinical environment for a plurality of reasons.

[0007] Most heart disease involves the left ventricle of the heart. Thispumping chamber is generally known as the workhorse of the heart. Apatient with a non-functioning right ventricle can survive quitesuccessfully provided that their pulmonary blood flow resistance is lowenough to allow circulation through the lungs and the rest of the bodyentirely as a result of the efforts of the left ventricle. However,collapse of the left ventricle is most often fatal. An LVAD is able tofully take over the function of this ventricle, thus perfusing the bodywith oxygen-rich blood. The LVAD attaches to the patient's naturalheart, and to a natural artery, and can be removed if the natural heartrecovers.

[0008] Blood flow in the LVAD is effected by expansion and contractionof a variable-volume chamber. One-way valves associated with the inflowand outflow ports of the LVAD provide for blood flow into thevariable-volume chamber during expansion, and for blood flow out of thischamber, usually to the ascending thoracic aorta. These one-way flowvalves may be constructed as part of the LVAD itself, or may be disposedin the blood-flow conduits which connect the LVAD to the heart andaorta. A pair of conduits respectively connect the inlet port of theassist device to the left ventricle and the outlet port to the majorartery which is to receive the blood flow from the device.

[0009] As described above, artificial blood conduits have become avaluable tool of modern medicine. One use of such artificial bloodconduits is as a temporary or permanent prosthetic artery. Another useis in the connection of temporary blood pumps, or ventricular assistdevices, between the left ventricle of the heart and a major artery. Insuch a use, the demands on the artificial blood conduit are great. Theartificial conduit must deal with the pulsatile blood flow created bythe host's own heart, as well as with the flow, pressure, and pulsationscreated by the assist device. The artificial conduit must functionwithin or outside of the host patient's body, and not introduce or allowthe entry of bacterial or other contamination into the host's body orcirculatory system. Also, the artificial conduit must be connected toboth the heart, or to a major artery of the host's circulatory system inorder to allow connection of both the artificial conduit, and also ofthe ventricular assist device or pump.

[0010] A persistent problem with artificial blood conduits has been theprovision of a valving device of the one-way type in these conduits sothat a ventricular assist device can achieve pulsatile blood flow inresponse to the expansion and contractions of a variable-volume chamberof the assist device.

[0011] A conventional artificial blood conduit is know in accord withU.S. Pat. No. 4,086,665, issued May 2, 1978, to Poirier. The bloodconduit of the Poirier patent is believed to include an internalconvoluted fabric tube of essentially circular cylindrical configurationthroughout its length. This inner fabric tube is carried within an outertube, which is also convoluted over part of its length. The inner tubeis porous while the outer tube is liquid impervious. A tri-foliatevalving structure is provided in the conduit to ensure unidirectionalblood flow in the conduit. This tri-foliate valving structure is taughtby the Poirier patent to be a porcine xenograft, sutured into the fabricof the inner tube. A circular support ring may be disposed outside ofthe inner tube wall to assist in support of the xenograft. Provision ismade for connection of the artificial blood conduit of Poirier to otherblood-carrying structure, and to the vascular tissue or heart tissue ofthe host via suture rings. Essentially, Poirier teaches that the valvedconduit may be connected to other blood-carrying structure by means offlanged connections using gasket-sealed interfaces and threaded collarswhich engage onto threaded portions of the adjacent conduit or otherblood-carrying structure.

[0012] With the artificial blood conduit taught by the Poirier patent,the conduit structure itself is quite bulky, being composed of severalconcentric structures or elements, some of which are spaced apartradially from one another. As a result, the Poirier conduit has aconsiderable wall thickness built up by all of these individual wallelements. Additionally, the inner lumen or passageway of this artificialconduit does not provide for elimination of blood flow stagnation orstasis downstream of the tri-foliate valve structure. Accordingly, thestagnant blood may clot or may adhere to the walls of the conduit, to beshed eventually as emboli in the circulatory system of the host. Also,the annular space between the inner porous conduit and the outerimpervious conduit may harbor bacterial contamination, and provide asite for bacterial growth and infection which is hidden from thepatient's immune system.

[0013] A conventional bio-material xenograft valve is known in accordwith U.S. Pat. No. 4,247,292, issued Jan. 27, 1981, to W. W. Angell. TheAngell patent is believed to disclose an externally-stented naturaltissue valve for heart implantation in which the natural xenografttissue is sutured to a fabric covered plastic stent. The valve issecured into a patient's heart by sutures between the suture ring andthe heart tissue. There is no artificial conduit which is valved by thedevice of Angell.

[0014] Another conventional artificial conduit is disclosed by U.S. Pat.No. 5,139,515, issued Aug. 18, 1992 to F. Robicsek. The Robicsek patentis believed to disclose an artificial aortic root portion which includesa convoluted wall formed with sinuses generally aligned with theleaflets of the natural tri-foliate valve of the patient's heart. As soconfigured, it is asserted that the blood flow “recoil” downstream ofthe valve leaflets will assist in their closing, resulting in a morenatural valve function, with reduced regurgitation. However, theartificial aortic root portion taught by Robicsek includesout-pouchings, or sinuses, which are themselves formed with corrugationsor convolutions like the rest of the artificial conduit. Theseconvolutions at the sinuses themselves may contribute to the formationof small localized turbulent zones, or to the formation of stasis orstagnation volumes where blood flow is slowed or stopped. In eithercase, the fluid flow dynamics of the artificial conduit suggested by theRobicsek patent is highly questionable because it may cause theformation of clots which are eventually shed as emboli in thecirculatory system.

[0015] Yet another artificial valve is known in accord with Britishpatent specification No. 1315845, of B. J. Bellhouse, the completespecification for which was published on May 2, 1973. The Bellhousespecification is believed to disclose an artificial valve forimplantation within the natural aortic root, with a ring part formed ofsilicone-coated uncut polyethylene terephthalate fabric. The cusps ofthis valve are formed of woven and/or knitted material of the same typeof polyethylene terephthalate fabric, which is also coated with siliconerubber. However, the valve of Bellhouse is implanted into the naturalaortic root, with the natural sinuses present, and does not include aprosthetic conduit for blood flow.

[0016] A persistent problem with all of the above-identifiedconventional devices, and with others which are known also in the art,is the rather high number of material-surface transitions, or changes inthe material across which the patient's blood must flow in passingthrough the devices. For example, in the artificial blood conduit ofPoirier, disclosed in the '665 patent, the flowing blood is exposed toat least nine different surfaces in flowing through this device. Thesedifferent surfaces include the tissue surfaces of the porcine xenograft,the sutures which secure this graft, the fabric inner conduit, thegasket surfaces at the ends of the valved conduit, and the endconnectors to which the fabric inner conduit connects. When the entireventricular assist device of Poirier is considered, several additionalblood-contacting surfaces of different materials, or material-surfacetransitions, must also be added to this list. Each of theseblood-contacting material-surface transitions represents a potentialsource of turbulence in the flowing blood if the adjacent surfaces donot align perfectly with one another.

[0017] Additionally, the flowing blood may not have the same affinityfor creating a stable biological interface with each of the variousmaterials. That is, the material surfaces may have a differing degreesof surface porosity, of surface roughness, of surface energy, or ofbio-compatibility with the host, for example. Consequently, with thepassage of time, the biological interface between the flowing blood andthe artificial, “not self” surfaces will be laid down withdiscontinuities, or with changes in tenacity of attachment to theunderlying artificial surfaces, for example, at these material-surfacetransitions in the device. Each of these discontinuities or changes intenacity of attachment of the biological interface with the underlyingartificial structure represents an opportunity for a portion of theinterface to slough off to become an emboli in the circulating blood.Also, blood may clot at these unstable interfaces, also representing arisk of forming emboli in the blood.

SUMMARY OF THE INVENTION

[0018] In view of the deficiencies of the conventional relatedtechnology outlined above, it is an object for this invention to providea ventricular assist device having a variable-volume chamber, and a pairof valved conduits connecting the variable-volume chamber to thecirculatory system of a patient, and in which the number ofblood-contacting material-surface transitions is minimized.

[0019] More particularly, the present invention has as an object theprovision of a ventricular assist device in which the variable-volumepumping chamber is formed of a single unitary blood-contacting flexiblewall member, and this wall member is sealingly contacted by the materialdefining the blood-contacting wall of the valved conduit itself, withoutthe use of gaskets or other sealing devices which are exposed to theflowing blood.

[0020] Still further to the above, the present invention has as anobject the provision of a valved conduit in which the flowing blood isexposed only to the surfaces of a prosthetic valve, such as a porcinexenograft valve, to the sutures which secure this valve, and to theinner porous surface of a fabric conduit communicating the patient'scirculatory system with the variable-volume chamber of the assistdevice.

[0021] Additionally, a further object of the present invention is toprovide such a ventricular assist device, and valved conduit for such adevice in which the fabric which defines the inner blood-contactingsurface of the valved conduit is internally porous, but is impermeableto blood. Consequently, the fabric of this conduit presents a veryfavorable surface upon which a stable biological interface may be laiddown by the flowing blood. On the other hand, this impervious fabricdoes not require an outer impervious conduit or tube like that used inthe Poirier '665 patent in order to prevent blood from seeping throughthe fabric. This impervious fabric conduit can then be disposed in aperforate cage or support structure which is outwardly exposed to bodyfluids. Because the cage and fabric conduit are outwardly exposed tobody fluids they do not provide a cavity or void in which a bacterialinfection may be hidden from the immune system, as may occur with thedevice taught by the Poirier '665 patent.

[0022] Still further, an object of the present invention is to providesuch a valved conduit in which the conduit is formed with sinusesdownstream of the tri-foliate prosthetic valve, such as a natural tissueporcine xenograft valve, and which sinuses do not replicate either thenatural porcine sinuses of the aortic root from which the valve isremoved, for example, or the natural human aortic sinuses. However,these sinuses are especially shaped and sized to cooperate with theprosthetic valve to ensure the formation of vigorous blood-flow vorticesbehind each valve leaf. These vortices in the flowing blood contributeto an improved valve action, and to prompt closing of the valve leafletsupon the systole ending, as is recognized in the art. However, thevigorous vortices provided by the present inventive sinus configurationof the valved conduit also ensures that the blood-exposed surfaces ofthe conduit are scrubbed by the flowing blood. Consequently, bloodstagnation or stasis is avoided, and clots do not form on the conduitwalls to be later sloughed off as emboli in the circulatory system.

[0023] Yet another object for the present invention is to provide such avalved conduit in which the prosthetic valve, such as a porcinexenograft valve, is externally stented with the fabric of the conduitinterposing between the material of the prosthetic valve and the stentstructure. Consequently, the prosthetic valve is supported effectivelyfor its operation to control the blood flow in the valved conduit to aunidirectional flow. The prosthetic valve is supported with superiorstrength to successfully resist the large pressure variations and rapidchanges in fluid flow involved with the ventricular assist device.Further, the flowing blood is not exposed to the surfaces of thestenting structure, the formation of clots in the blood on additionalblood-exposed surfaces is thus avoided and is reduced. That is, thestent structure is entirely removed from and is isolated from theflowing blood.

[0024] Accordingly, the present invention provides a ventricular assistdevice including a unitary flexible wall member having a singularblood-contacting inner surface entirely defining a variable-volumechamber for receiving and discharging blood, the unitary flexible wallmember also defining one of an inlet port and an outflow port forrespective flow of blood, and a flexible conduit member having a sidewall defining a second blood-contacting inner surface and communicatingblood between the variable-volume chamber and the circulatory system ofa host organism, the side wall of the flexible conduit member sealinglyengaging the unitary flexible wall member at the respective one of saidinlet and outflow ports so that flowing blood in passing through saidflexible conduit and said variable-volume chamber contacts only thefirst and the second blood-contacting inner surfaces.

[0025] According to a further aspect of the present invention, a valvedconduit is formed of fabric sheet material having an outer surfacethereof coated with impermeable polymeric material partiallyimpregnating into the intersticial spaces of the fabric between fibersthereof toward but short of the inner surface of the fabric conduit.

[0026] Still another aspect of the present invention provides a valvedconduit for a ventricular assist device including a prosthetic valve,such as a natural tissue porcine xenograft valve, defining a firstblood-contacting surface, a fabric conduit in which the prosthetic valveis secured and defining a second blood-contacting surface, and suturessecuring the prosthetic valve into the fabric conduit and defining athird blood-contacting surface, the valved conduit having only thefirst, the second, and the third blood-contacting surfaces which contactblood flowing through said conduit.

[0027] The present invention provides according to another aspect avalved conduit including a porcine xenograft valve and defining sinusesdownstream of the valve which sinuses do not replicate either theporcine sinuses or human sinuses, and which by their configurationensure that blood flow past the leaflets of the valve forms vigorousvortices behind these leaflets without blood stagnation.

[0028] Still further, the present invention provides a valved conduit inwhich a resilient connection is provided between the valved conduit andadjacent blood-carrying structures. This resilient connection providesfor all of post-implantation absorption of a collagen or otherbiodegradable transitional coating from the inner surfaces of the valvedconduit with attendant dimensional changes, for the subsequent formationof a stable biological interface on these surfaces also possibly withattendant change of dimensions, and for components of the valved conduitand adjacent structure taking a set with the passage of time aftersurgical implantation, all without loss of sealing integrity between theconnected structures. Such a loss of sealing integrity could create aleakage path at the interface of the valved conduit and an adjacentstructure.

[0029] Additionally, the present invention provides such a valvedconduit which is interfaced with adjacent blood-carrying structure by apolarized connection both preventing incorrect assembly of the valvedconduit to the adjacent structure, and preventing damage to the conduitor adjacent structure from the application of excessive tighteningforce, while also accommodating changing dimensions as components of thevalved conduit and adjacent structure take a set with the passage oftime after surgical implantation.

[0030] Additional objects and advantages of the present invention willbe apparent from a reading of the following detailed description of asingle preferred embodiment of the present invention, taken inconjunction with the appended drawing Figures, in which the samereference numeral refers to the same feature in each of the variousviews, or to features which are analogous in structure or function.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0031]FIG. 1 is a fragmentary frontal elevational view diagrammaticallydepicting a ventricular assist device according to the present inventionimplanted in a human host patient;

[0032]FIG. 2 provides a fragmentary cross sectional view of a portion ofthe ventricular assist device seen in FIG. 1, with a portion of theexternal housing of the device removed for clarity of illustration;

[0033]FIG. 3 provides a fragmentary exploded perspective view of theventricular assist device with valved conduits thereof separated from apump portion of the device in order to more clearly show a polarizedconnection structure for each of the valved conduits;

[0034]FIGS. 4 and 5 show respective longitudinal cross sectional viewstaken through the inflow and outflow valved conduits of the ventricularassist device of the present invention;

[0035]FIG. 6 provides a greatly enlarged fragmentary cross sectionalview taken through the inflow conduit connection with the pump portionof the present assist device;

[0036]FIG. 7 provides an enlarged transverse sectional view taken atline 7-7 of FIG. 4;

[0037]FIG. 8 provides an enlarged fragmentary longitudinal crosssectional view taken along line 8-8 of FIG. 7;

[0038]FIG. 9 is a somewhat diagrammatic presentation of a step in theprocess of manufacturing a valved conduit according to the presentinvention;

[0039]FIG. 10 is a somewhat diagrammatic and cross sectional view of astep of the manufacturing process for making a valved conduit accordingto the present invention, and is subsequent to the step seen in FIG. 9;

[0040]FIG. 11 is a greatly enlarged and somewhat schematicrepresentation of an inwardly porous, but blood-impermeable, fabricresulting from the manufacturing steps seen in FIGS. 9 and 10, and whichforms a wall of the valved conduit of the present invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTION

[0041] With reference first to FIG. 1, a living human host patient 10 isshown in fragmentary front elevational view, and with parts of thepatient's anatomy shown in phantom or removed solely for betterillustration of the salient features of the present invention. It willbe understood that the human host patient 10 preferably has a completeanatomy, and that the use of the present invention does not generallyrequire that any part of the patient's normal anatomy be removed, asmight be suggested by FIG. 1.

[0042] Surgically implanted into the patient's abdominal cavity 12 isthe pumping portion 14 of a ventricular assist device, generallyreferenced with the numeral 16. The ventricular assist device 16includes an inflow conduit 18 communicating blood from the patient'sleft ventricle into the pumping portion 14, and an outflow conduit 20communicating blood from the pumping portion 14 to the patientsascending thoracic aorta. At the end of the inflow conduit 18 which isconnected to the patient's heart, and at the end of the outflow conduit20 which is connected to the ascending thoracic aorta, these conduitsare attached to the natural tissues by suture rings so that blood flowcommunication is established and maintained. From the pumping portion 14a power cable 22 extends outwardly of the patient's body via an incision24 to a compact controller 26. A power source, such as a battery packworn on a belt about the patient's waist, and generally referenced withthe numeral 27, is connected with the controller 26.

[0043] Viewing FIG. 2, it is seen that the pumping portion 14 includes ahousing 28 within which is received a flexible unitary liner or bagmember 30. This bag member 30 defines a singular blood-contacting innersurface 32, bounding a variable-volume chamber 34. The bag member 30includes a diaphragm portion (not shown) which is reciprocally movablein response to reciprocating movements of a power member (referencedgenerally with the numeral 14′) of the pumping portion 14 to expand andcontract the variable-volume chamber 34. As FIG. 2 illustrates, the bagmember 30 also defines tubular leg portions 36, 38, extending to andthrough respective inlet and outlet fitting features 40, 42 of thehousing 28. At each of the inlet and outlet fitting features 40, 42, ofthe housing 28, the tubular legs 36, 38 form reentrant portions 44, eachof which is generally J-shaped in cross section. At the inlet and outletfitting features 40, and 42, the housing 28 includes structuralprovisions allowing connection and disconnection of the respectiveinflow and outflow conduits 18, 20, as will be further described.

[0044] Importantly, as FIG. 2 shows, each of the inflow and outflowconduits 18, 20, respectively includes a tubular flexible, butshape-retaining fabric-composite inner wall member 46, having an innerblood-contacting surface 48. As will be further explained, the innerblood-contacting surfaces 48 of the conduits 18 and 20 each also definesa respective reentrant end portion 50. The reentrant end portions 50 arealso J-shaped in cross section. As is seen in FIG. 2, the reentrant endportions 50 of the conduits 18 and 20 sealingly contact the reentrantportions 44 of the bag member 30. These sealingly contacting reentrantportions 44 and 50 cooperatively define a sealing line 51. Consequently,the flowing blood in moving from the inflow conduit 18 to the bag 30,and from this bag to the outflow conduit 20, crosses only twomaterial-surface transitions. The first of these material-surfacetransitions is from the surface 48 of the inner wall member 46 at theinflow conduit 18 to the surface 32 of the bag 30, the second of thesematerial-surface transitions is from the surface 32 to the surface 48 ofthe conduit 46 at the outflow conduit 20. As will be further describedand explained, this minimizing of material-surface transitions which areexposed to flowing blood in the ventricular assist device 16 is aconsistent feature throughout the device.

[0045]FIG. 3 provides a fragmentary exploded perspective view of thepumping portion 14, and of the two blood flow conduits 18, and 20, asthey may appear, for example, during surgical implantation of the assistdevice 16. FIG. 3 illustrates that as part of the fitting features 40and 42, the housing 28 defines a respective inflow port 52 and arespective outflow port 54, each with a respective female threadedrecess 56 leading to the corresponding one of the exposed reentrantportions 44 of the bag 30. These threaded recesses 56 are in mostrespects identical with one another. That is, they define the samediameter, and have the same type and pitch of screw thread. However, thefluid flow configuration of the pumping chamber 34, and of thetransitions of the legs 36 and 38 into and from this chamber, isdifferent for the inflow port than for the outflow port because of thediffering pressure and momentum conditions for the flowing blood passingthrough these leg portions of the bag 30. Accordingly, the physicianmust properly connect the inflow conduit 18 to the inflow port 52, andthe outflow conduit 20 to the outflow port 54.

[0046] In order to insure that the implantation physician does notmistakenly connect the conduits, each conduit includes a respectiveexclusive-fitting key feature 58, 60. The inflow conduit key feature 58includes four axially extending and circumferentially evenly spaced keyelements 62. At the inflow port 52, the recess 56 of housing 28 definesfour matching slots 64. The outflow conduit key feature 60 includes fiveaxially extending and circumferentially evenly spaced key elements 66.At the outflow port 54, the recess 56 of housing 28 defines fivematching slots 68. Each of the conduits 18, 20 includes a knurled andmale-threaded connector collar 70, which is freely rotatable on the endof the conduit to be connected to the pump housing 28. This collar 70 isthreadably receivable into the recesses 56. Consequently, the physiciancan connect the valved conduits 18, 20 to the housing 28 of the pumpingportion 14 of the assist device by feel alone if necessary.

[0047] That is, in the environment of the surgical implantation, thephysicians need not rely on color coding or some other visual device toassure themselves that the conduit connections are being effectedcorrectly. The conduits 18, 20 will mate with the housing 28 only in theproper location, and this proper mating of the conduits with the housingcan be determined by the tactile feel of the keys 62 and 66 droppinginto the slots 64 and 68 when the connections are made properly. Whenthese proper connections are made, then the threaded collars 70 willthreadably engage the threads of the corresponding recess 56 to retainthe conduit connections.

[0048]FIGS. 4 and 5 provide respective axial cross sectional viewsthrough the respective inflow and outflow conduits 18 and 20. Becausemany of the features of these two conduits are the same, they aredescribed together, and the same reference numeral is used with respectto features of each which are the same or which are analogous instructure or function to one another. Each of the conduits 18, 20includes a tubular metallic housing 72. This housing is flanged at 74,and defines an outward cylindrical portion 76 upon which the collar 70is rotationally carried, viewing also FIG. 6. Interposed between thecollar 70 and the flange 74 is a circumferentially extending wave washer78, the purpose of which will be described below. However, viewing FIGS.4 and 5, and recalling the description above, it is apparent that whenthe collars 70 are threaded into the recesses 56 of the housing 28 theyconfront the flanges 74 to retain the conduits 18, 20, with thereentrant end portions 50 in sealing engagement with the reentrantportions 44 of bag 30 to define the singular sealing lines 51. Thehousings 72 define plural perforations 73, in the form of slots, toallow body fluid to access the internal surfaces of these housings andavoid the formation of cavities or voids which are hidden from theimmune system.

[0049] At the end of each housing 72 of conduits 18, 20 distally fromthe pumping portion 14, a male-threaded portion 80 circumscribes atapered seating feature 82. On the tapered seating feature 82 with aninterposed radially extending annular portion 84 of the inner wall 46 issealingly connected the adjacent end 86 of an elongate flexiblepolyethylene terephthalate fabric blood conduit 88. The conduits 88 leadto the pumping portion 14 from the patient's left ventricle, and fromthis pumping portion to the patient's ascending aorta. The ends of theseconduits 88 remote from the pumping portion 14 are sutured to the heartand aorta at appropriate incisions in each to achieve communication ofthe conduits 18, 20, and of the pumping portion 14 with the patient'scirculatory system. The end 86 of the conduit 88, and the portion 84 ofinner wall 46 sealingly engage one another to cooperatively define thesealing line 89.

[0050] Around the polyethylene terephthalate fabric blood conduit 88 isa flexible plastic sheath 90. This plastic sheath 90 defines an endshoulder 92, and rotationally carries an internally-threaded collar 94.Collar 94 threadably engages the thread portion 80 of the housing 72 tomaintain sealing engagement of the conduit 88 with the portion 84 of theinner wall 46 at the tapered seating feature 82. Interposed between thecollar 94 and the end shoulder 92 is a circumferentially extending wavewasher 96. On the inner surface of each polyethylene terephthalatefabric blood conduit is a thin bio-compatible collagen coating,indicated with arrowed lead line 98. This collagen coating serves tomake the polyethylene terephthalate fabric conduit 88 more leakresistant at the time of implantation, and also more compatible with thepatient's blood.

[0051] However, this collagen coating 98 is biodegradable, and iseventually absorbed by the patient's body. At the same time that thecollagen coating 98 is being absorbed by the patient's body, abiological interface is deposited on the inner surfaces of the conduits88. As the collagen coating 98 is absorbed from the area of conduit 88at the end 86 seating on wall portion 84 and seating feature 82, thedimensions of the conduit 88 may decrease slightly. This slight changeof dimension could lead to a blood seepage at the connection of thepolyethylene terephthalate fabric conduits 88 to the metallic housings72 perhaps weeks or months after the surgical implantation of the assistdevice 16. To avoid this possibility, the wave washer is provided sothat the connection between the conduits 88 and the housings 72 has anaxial resilience accommodating changes in thickness dimensions of theconduits. Also, this axial resilience provides for maintenance ofsealing engagement between the conduits 88 and the housings 72 as theseparts take a set over time following implantation.

[0052] With attention now more particularly to the fabric-compositetubular inner wall member 46, it will be noted that this inner wallmember defines the inner surface 48, which extends continuously betweenand is integral with the reentrant end portion 50 at the housing 28(which is sealingly engaged by bag member 30 at sealing line 51) and theradially extending portion 84 (which is sealingly engaged by the fabricconduit 88 at sealing line 89). This inner surface 48 defines theblood-contacting boundary for the conduits 18, 20. Within this innersurface 48, and secured to the fabric of the fabric-composite inner wallmember 46, and to an external stent structure 100, is a porcinexenograft tri-foliate valve 102. It will be understood that other typesof prosthetic valve may be used in the conduits 18 and 20. For example,one type of prosthetic valve now available is fashioned from a sheet ofeither animal or human tissue, or from artificial material. This andother types of prosthetic valves may be used in the present invention.This xenograft valve defines tissue surfaces 104. In the inflow conduit18, the valve 102, and supporting stent structure 100, are disposed forunidirectional blood flow toward the chamber 34. In the outflow conduit,the valve 102 and supporting stent structure 100 are oppositelydisposed. The porcine xenograft valve 102 is secured to the inner wall46 and to stent structure 100 by sutures 106. Accordingly, it is seenthat blood flow through the conduits 18, 20, contacts only the innersurface 48 of conduit 46, the tissue surface 104 of the xenograft valve102, and the sutures 106.

[0053] Returning to a consideration of FIG. 6, it is seen that withinthe recess 56, the housing 28 also defines an additional annular recess108. Disposed in this recess 108 is an annular elastomeric sealingmember 110. When the conduit 18 or 20 is received into the respectiveone of the recesses 56, the reentrant portion 50 of the inner wallmember 46 sealingly engages with the reentrant portion 44 of the pumpingbag member 30. This sealing interface is inwardly exposed to flowingblood. However, radially outwardly of the sealing interface of surfaces44 and 50, the sealing member 110 is sealingly engaged by an end edgesurface 112 of the housing 72 in order to provide a redundant secondarysealing interface between the conduits 18, 20 and the housing 28. Thissecondary sealing feature (member 110 and metallic end edge surface 112)is not exposed to flowing blood. Also, as is seen in FIG. 6, the housing28 at recess 56 defines a slot 64 for receiving a respective one of theexclusive-fitting keys 62. This same feature is found at the recess 56for the conduit 20, recalling that the number of keys, and slots forthese keys, differs between the recess 56 for inflow conduit 18 and therecess 56 for outflow conduit 20.

[0054] Returning to consideration of FIGS. 4 and 5, immediatelydownstream of the xenograft valve 102, the tubular inner wall member 46defines three out-bulgings, or sinuses 114. These sinuses 114 arealigned axially with each one of the three valve leaflets of the valve102, viewing also FIGS. 7 and 8. As is understood in the art, a sinus atthis location having a downstream termination which is located somewhatdownstream of the leaflets in their open positions (viewing FIG. 8),promotes the entry into the sinuses of a flow vortex 116 formed at thedownstream end of the valve leaflets. This vortex flow contributes to aprompt closing of the valve at the end of the systole with littleregurgitation.

[0055] However, the natural porcine or human sinuses are considerablylarger than the Applicants have determined to be optimum for use withthe prosthetic valve 102. In fact, the natural human sinuses at theaortic valve form a circular boundary with the valve leaflet if viewedin an oblique plane extending perpendicularly to the axis of the leafletsurface. Also, in a transverse plane the natural human sinuses arepouch-like and at their maximum dimension define a diameter almost twicethe diameter of the aorta. The sinuses 114 of the conduits 18 and 20 aresmaller than natural sinuses, and rejoin the generally cylindricaltubular inner wall member 46 at an acute or glancing angle, indicatedwith the arrowed lead line 118. Further, the sinuses 114 are longer andshallower than natural sinuses, as is explained below.

[0056] More particularly, if the inner valve leaflet radius at the baseof the tri-foliate valve 102 is referred to as R_(b), and the radius atmaximum dimension of the sinuses 114 is referred to as d_(s), with thelength of the sinuses 114 from the attachment of the valve leaflets tothe rejoining of the sinus wall with the projected cylindrical shape ofthe remainder of the inner wall 46 (i.e., at the arrow 112) beingreferred to as h_(s) (viewing FIGS. 7 and 8), then for natural sinusesof several mammalian species, including rabbits, canine, Ox, sheep,calf, pig, and human an aspect ratio of h_(s) divided by d_(s) can becalculated. The dimensions of usual aortic valves for these species isfound in the literature. It is seen that the ratio value naturallyranges from 0.71 to 1.2. For the conduits 18 and 20, the aspect ratio ofthe sinuses 114 is in the range from at least about 1.3 to about 1.6 ormore. More preferably, the aspect ratio for the sinuses 114 is about1.45.

[0057] The Applicants have determined that the above-described range ofsinus aspect ratios is preferable for achieving vigorous vortex bloodflow downstream of the valve 102 in the inflow conduit 18, withresulting elimination of blood stasis or stagnation. Blood flow into thepumping portion 14 via this conduit 18 results merely from the naturalblood pressure prevailing in the circulatory system of the host patient10. The variable-volume pumping chamber 34 does not effectively aspirateblood into this chamber by expansion. Instead, blood flows by its ownpressure through the conduit 18 and into this chamber, expanding thechamber 34. Accordingly, the inflow of blood via conduit 18 iscomparatively slow. The increased aspect ratio of the conduit 18 incomparison with the natural sinuses is important to the prevention ofclot formations in the conduit 18.

[0058] On the other hand, the blood flow out of pumping chamber 34 isforceful and vigorous. A sinus configuration at conduit 20 whichreplicated the natural sinuses might be acceptable. However, as pointedout above, the natural sinuses are more bulged out and take up moreroom. The sinus shape of the present invention with an aspect ratio ofat least 1.3 or higher, when used also at the outflow conduit 20,results in an outflow conduit of smaller diameter, reduces the size ofthe apparatus implanted into the host patient 10, and serves very wellto promote vigorous blood vortex flow downstream of the valve 102without the formation of clots in the conduit 20.

[0059] As will be further explained, the tubular fabric-composite innerwall member 46 is formed with the sinuses 114, and with adjacent arcuatetransition portions 120, transitioning between a downstream edge 122 ofthe xenograft valve 102 and the sinuses 114, viewing FIGS. 4 and 5.These transition portions 120 allow the xenograft valve 102 to beexternally stented with the stent structure 100 being located outside ofthe flexible fabric tubular inner wall member 46, while still providinga smooth surface for blood flow transition from the xenograft valve 102,to the surface 48 of the wall member 46 downstream of the valve 102. Thestent structure 100 includes a metallic wire-form 124 having threeaxially-extending commissure support parts, which are not visible in thedrawing Figures, but which align with and follow the shape of thenatural commissures 126 of the porcine xenograft valve 102. Received inthe wire-form 124 is a polyester support member 128. Around thewire-form 124, and the support member 128, is formed a fittedpolyethylene terephthalate fabric drape 130. The polyethyleneterephthalate fabric drape 130 is formed closely to the wire-form 124and support member 128. However, sutures 106 engage this drape 130 andthe underlying wire-form 124, pass through the corresponding inner wallmember 46, and secure the tissue xenograft valves 102 in the conduits18, 20, respectively. The fabric composite inner wall member 46 is alsoformed with very slight recesses between the sinuses 114, which recessesaccommodate the radial thickness of the commissures of the wire-form124.

[0060] Considering now FIGS. 9, 10, and 11, the first two of theseFigures show steps in the process of making a flexibly shape-retainingfabric-composite tubular inner wall member 46 for a valved conduit, suchas conduit 18 or 20. FIG. 11 shows a greatly enlarged cross sectionalview through the fabric-composite tubular inner wall member 46. As FIG.11 shows, this inner wall member 46 includes a single ply oftubular-woven and/or knitted polyethylene terephthalate fabric 132. Eventhough this woven and/or knitted fabric 132 is of made of fine-dimensionfibers, and is closely woven or knitted, it nevertheless is liquidpermeable. Consequently, the fabric 132 is porous, and must beconsidered to be substantially blood permeable. However, in order torender the inner fabric composite wall 46 substantially bloodimpermeable while still providing a porous inner surface 48 to which astable biological interface may attach, the tubular fabric 132 istransfer-coated externally with sheet silicone rubber material 134.

[0061] As FIG. 11 shows, this silicone rubber 134 is permeated inwardlyinto and partially through the woven or knitted fabric 132, toward butshort of the inner surface 48 of this fabric. The silicone rubber 134 isaxially and circumferentially continuous, so that it forms aliquid-impermeable barrier or membrane integral with the fabric 132, andan integral part of the inner wall member 46. Inwardly of this siliconerubber 134, the woven and/or knitted fabric 132 through a part of itsthickness still forms a filamentary permeable structure providing aporous inner surface (i.e., the inner surface 48 of the conduit 46),into which a stable biological interface may implant. This surface 48 isstill porous like conventional woven and/or knitted polyethyleneterephthalate fabric vascular grafts, but the porosity of the fabric nolonger extends completely through the thickness of the fabric 132.

[0062] Viewing FIG. 9 it is seen that the tubular woven and/or knittedfabric 132 in a limp cylindrical configuration without the siliconerubber 134, sinuses 114 or other features, is placed on a cylindricalmandrel 136. Adjacent to this mandrel 136 is disposed a cylindricalroller 138 with a smooth hard surface. On the roller 138 is disposed asheet 140 of raw silicone rubber material. The mandrel 136 and roller138 are pressed together (indicated by arrows 142) while being rotatedin unison (indicated by arrows 144) to transfer the silicone rubbersheet material 140 onto and into the woven and/or knitted fabric 132. Bycontrol of the state of the silicone rubber material of sheet 140 (i.e.,its degree of partial curing), and the amount of pressure applied, thedegree or depth of penetration of the silicone rubber material into thewoven or knitted fabric 132 is controlled. The woven or knitted fabricmaterial 132 and silicone sheet material 140 are then removed togetherfrom the mandrel 136. Subsequently, the silicone material 140, which isa thermoset material, is completely, or substantially completely curedto produce as a manufacturing intermediate article or work piece, acylindrical sleeve of woven or knitted fabric outwardly coated andpartially impregnated with silicone rubber.

[0063] Next, the work piece including the cylindrical woven or knittedfabric sleeve 132 and silicone rubber 140, referred to in FIG. 10 withthe composite reference numeral 132/140, is placed into a heatedfemale-cavity mold 146. This mold 146 defines a cavity 148 generallymatching to the cylindrical shape of the work piece 132/140, but alsohaving radially outwardly extending recesses 150 corresponding to thesinuses 114, slight indentations between the recesses 150 foraccommodation of the commissures of the wire-form 124, and one or morecircumferential grooves or diametral steps 152, which will form thereentrant surface 50 or annular portion 84 of the fabric-composite innerwall member 46, recalling FIGS. 4 and 5. Into the cavity 148 and withinthe tubular work piece 132/140 is placed a thin-walled high-pressureexpansible balloon 154. This balloon is made of an elastomeric material,such as a vulcanized natural or synthetic rubber, which is able towithstand both an elevated temperature and internal pressure. Theballoon 154 is inflated by applying an internal pressure (indicated witharrow 156) to force the work piece 132/140 against the inner surfaces ofthe cavity 148.

[0064] Even though the silicone rubber 140 of the work piece 132/140 isa thermoset material, and is at least substantially cured, thepolyethylene terephthalate fabric 132 is a thermoplastic material.Consequently, the work piece 132 takes on and retains a shapereplicating the internal shape of the cavity 148. The cavity 148 iscooled, the balloon 154 is deflated to return it to its original sizefor removal from the cavity 148, and the work piece is removed from thiscavity. Although the polyethylene terephthalate fabric material 132 is athermoplastic material and is changed in shape by the above-describedprocess, at least in the area of the sinuses and at the features 50 and84 of the inner fabric composite wall member 46, the penetration orimpregnation of the silicone rubber 140 partially through this fabric issubstantially not changed. The silicone rubber was cured fully orsubstantially enough before this shaping step so that the siliconerubber is no longer mobile in the fabric 132 of the work piece 132/140.This work piece 132/140, having woven and/or knitted fabric 132 withsilicone rubber liquid barrier 134, is substantially ready for use inmaking the fabric composite inner wall member 46. Subsequently, the workpiece 132/140 is trimmed to fit into the conduit 18 or 20, the xenograftvalve 102, and stent 100 is added, and the combination is placed intothe housing 72 and completed at the ends for sealing cooperation withthe pump portion 14 and conduits 88, as described above.

[0065] While the present invention has been depicted, described, and isdefined by reference to a particularly preferred embodiment of theinvention, such reference does not imply a limitation on the invention,and no such limitation is to be inferred. The invention is capable ofconsiderable modification, alteration, and equivalents in form andfunction, as will occur to those ordinarily skilled in the pertinentarts. The depicted and described preferred embodiment of the inventionis exemplary only, and is not exhaustive of the scope of the invention.Consequently, the invention is intended to be limited only by the spiritand scope of the appended claims, giving full cognizance to equivalentsin all respects.

We claim:
 1. A ventricular assist device comprising: a pumping portionincluding a unitary flexible wall member having a singularblood-contacting inner surface entirely defining a variable-volumechamber for receiving and discharging-blood, said unitary flexible wallmember also defining one of an inflow port and an outflow port forrespective flow of blood to and from said variable-volume chamber; and aflexible conduit member having a side wall defining a secondblood-contacting inner surface, said flexible conduit membercommunicating blood between the variable-volume chamber and thecirculatory system of a host organism, said side wall of said flexibleconduit member sealingly engaging said unitary flexible wall member at arespective one of said inflow and outflow ports; whereby flowing bloodof said host organism, in passing through said flexible conduit and saidvariable-volume chamber of said pumping portion, contacts only the firstand the second blood-contacting inner surfaces.
 2. The ventricularassist device of claim 1 further including a prosthetic valve disposedwithin said flexible conduit member for limiting blood flow therein to asingle direction, and a stenting structure for said prosthetic valvedisposed outside of said flexible conduit member.
 3. The ventricularassist device of claim 2 further including sutures attaching saidprosthetic valve to said stenting structure through said side wall ofsaid flexible conduit member, whereby blood flowing through saidflexible conduit member contacts only said second blood-contacting innersurface, said prosthetic valve, and said sutures.
 4. The ventricularassist device of claim 2 wherein said prosthetic valve is a naturaltissue xenograft valve.
 5. The ventricular assist device of claim 4wherein said natural tissue xenograft valve is a porcine xenograft. 6.The ventricular assist device of claim 2 wherein said prosthetic valveincludes at least a pair of valve leaflets, said flexible conduit memberfurther defining a like number of sinuses downstream of and axiallyaligning with said prosthetic valve leaflets.
 7. The ventricular assistdevice of claim 6 wherein said sinuses of said flexible conduit aresmaller than human natural aortic valve sinuses.
 8. The ventricularassist device of claim 6 wherein said sinuses of said flexible conduitdefine a portion of said second blood-contacting surface, and downstreamof said prosthetic valve said sinus-portion of said second surfacerejoins at an acute glancing angle a substantially-cylindrical remainderportion of said second surface.
 9. The ventricular assist device ofclaim 6 wherein said sinuses of said flexible conduit have an aspectratio of at least 1.3.
 10. The ventricular assist device of claim 9wherein said sinuses of said flexible conduit have an aspect ratio inthe range from about 1.3 to about 1.6 or more.
 11. The ventricularassist device of claim 6 wherein said sinuses of said flexible conduithave an aspect ratio of substantially 1.45.
 12. The ventricular assistdevice of claim 1 additionally including an elongate conduit memberconnecting with said flexible conduit member, said elongate conduitmember at one end thereof fluidly communicating with said hostorganism's circulatory system and at an opposite end fluidlycommunicating with said flexible conduit member to communicate bloodfrom said host's circulatory system to or from said variable-volumechamber, said inner wall of said flexible conduit member directlysealingly engaging said elongate conduit member at an end of the latter.13. The ventricular assist device of claim 1 further including a tubularhousing supportingly receiving said flexible conduit member, saidhousing defining at least one perforation therethrough outwardlyexposing said flexible conduit member to body fluids of said hostorganism.
 14. The ventricular assist device of claim 13 additionallyincluding means for resiliently retaining said flexible conduit memberin sealing engagement with said flexible wall member at said respectiveone of said inflow or outflow ports.
 15. The ventricular assist deviceof claim 14 wherein said means for resiliently retaining sealingengagement of said flexible conduit member with said flexible wallmember includes said pumping portion having a respective housingdefining a recess into which said flexible conduit and tubular housingthereof is received to sealingly engage said flexible wall member, saidtubular housing carrying means for engaging and securing axially withsaid pump portion housing and urging said flexible conduit into sealingengagement with said flexible wall member, and resilient meansinterposing axially between said means for engaging and said tubularhousing for allowing a limited amount of axial relative movementtherebetween.
 16. The ventricular assist device of claim 15 wherein saidmeans for resiliently retaining sealing engagement of said flexibleconduit member with said flexible wall includes said tubular housingrotationally carrying a collar which threadably engages into said recessof said pump portion housing to urge a flange portion of said tubularhousing into engagement with said pump portion housing, and acircumferentially extending axially-resilient washer member interposedaxially between said collar and said flange of said tubular housing. 17.The ventricular assist device of claim 16 wherein said axially-resilientwasher member includes a metallic wave washer.
 18. The ventricularassist device of claim 12 further including said elongate conduit memberincluding on an inner blood-contacting surface thereof a bio-degradableorganic coating for rendering said elongate conduit initially more leakresistant post-implantation with respect to blood loss from saidorganism's circulatory system.
 19. The ventricular assist device ofclaim 18 wherein said tubular housing further includes means forsealingly connecting with said elongate conduit member while sealinglyaccommodating change of dimension thereof as said biodegradable coatingis absorbed by said host organism.
 20. The ventricular assist device ofclaim 19 wherein said means for sealingly connecting includes saidtubular housing defining a tapered seating feature to which an end ofsaid elongate conduit sealingly connects, a shoulder on said elongateconduit, and a threaded ring engaging both said shoulder and saidtubular housing to threadingly urge said elongate conduit into sealingengagement with said seating feature, and an axially-resilient washermember interposing axially between said shoulder and said ring to takeup axial dimension lost by said elongate conduit in response toabsorption of said bio-degradable coating.
 21. The ventricular assistdevice of claim 20 wherein said axially-resilient washer member includesa metallic wave washer.
 22. A shape-retaining flexible conduit forcarrying blood in a living organism, said conduit comprising: fabricsheet material defining a tubular body having an inner surface boundinga flow path for said blood and an outer surface, at said outer surfacesaid tubular body carrying an impermeable coating ofbiologically-compatible polymeric material penetrating into said fabrictoward but short of said inner surface, said impermeable polymericcoating being continuous axially and circumferentially to render saidtubular body impervious to blood, and said inner fabric surfaceremaining porous to provide for attachment of a stable biologicalinterface thereon.
 23. The flexible conduit of claim 22 furtherincluding valve means disposed in said conduit flow path for limitingblood flow therein to a single direction.
 24. The flexible conduit ofclaim 23 wherein said valve means includes a prosthetic valve.
 25. Theflexible conduit of claim 24 wherein said prosthetic valve is a porcinexenograft.
 26. The flexible conduit of claim 23 further including astenting structure for supporting said valve means, said stentingstructure being disposed outside of said polymeric coating and beingisolated thereby from contact with said blood.
 27. The flexible conduitof claim 24 wherein said prosthetic valve includes at least a pair ofvalve leaflets, said flexible conduit member further defining a likenumber of sinuses downstream of and axially aligning with saidprosthetic valve leaflets.
 28. The flexible conduit of claim 27 whereinsaid sinuses of said flexible conduit are smaller than human naturalaortic valve sinuses.
 29. The flexible conduit of claim 28 wherein saidsinuses of said flexible conduit define a portion of said inner surface,and downstream of said prosthetic valve said sinus-portion of said innersurface rejoining at an acute glancing angle a substantially-cylindricalremainder portion of said inner surface.
 30. The flexible conduit ofclaim 28 wherein said sinuses have an aspect ratio of at least 1.3. 31.The flexible conduit of claim 30 wherein said sinuses have an aspectratio in the range from about 1.3 to about 1.6 or more.
 32. The flexibleconduit of claim 31 wherein said sinuses have an aspect ratio ofsubstantially 1.45.
 33. A valved prosthetic conduit for carrying aunidirectional blood flow in a living organism, said valved conduitcomprising: a natural-tissue xenograft valve defining a firstblood-contacting surface; a fabric conduit in which said valve issecured and defining a second blood-contacting surface; and suturessecuring said xenograft-tissue valve into said fabric conduit anddefining a third blood-contacting surface; whereby the valved conduithas only the first, the second, and the third blood-contacting surfacescontacted by blood flowing through said conduit.
 34. The valved conduitof claim 33 further including a stenting structure for said xenograftvalve, said stenting structure being disposed outside of said fabricconduit.
 35. The valved conduit of claim 34 wherein said fabric conduitis impervious to blood, and said fabric conduit isolates said stentingstructure from blood contact.
 36. The valved conduit of claim 33 whereinsaid fabric conduit is flexible and shape-retaining, said fabric conduitdefining plural sinuses downstream of said xenograft valve, and saidplural sinuses being the same in number and aligning axially with thenatural valve leaflets of said xenograft valve.
 37. The valved conduitof claim 36 wherein said plural sinuses differ from both the naturalsinuses from which said xenograft valve was removed, and from naturalhuman sinuses.
 38. The valved conduit of claim 37 wherein said sinusesof said flexible conduit are smaller than human natural aortic valvesinuses.
 39. The valved conduit of claim 38 wherein said sinuses have anaspect ratio of at least 1.3.
 40. The valved conduit of claim 39 whereinsaid sinuses have an aspect ratio in the range from about 1.3 to about1.6 or more.
 41. The valved conduit of claim 40 wherein said sinuseshave an aspect ratio of substantially 1.45.
 42. A method of making aflexible shape-retaining blood-impermeable fabric conduit member with aporous inner surface for use in carrying blood within a living organismand providing for formation of a stable biological interface on saidporous inner surface, said method comprising the steps of: forming atubular porous fabric body having an inner surface and an outer surface;on said outer surface applying a continuous coating ofbiologically-compatible blood-impervious polymeric material into saidfabric toward but short of said inner surface while maintaining porosityof said inner surface; employing said coating of polymeric material torender said tubular fabric body impermeable to blood flow; and formingsaid fabric conduit member from said fabric body coated with saidpolymeric material.
 43. The method of claim 42 including the steps ofusing a thermoset material as said blood-impervious polymeric material,and curing said thermoset material sufficiently to prevent furthermobility of said polymeric material in said fabric before forming saidconduit member therefrom.
 44. The method of claim 43 further includingthe steps of using a rotational cylindrical mandrel to support saidtubular porous fabric body, pressing a movable support surface againstsaid tubular porous fabric body on said mandrel, and feeding a sheet ofraw polymeric material between said fabric and said movable supportsurface as the latter and said mandrel are moved in unison.
 45. Themethod of claim 43 additionally including the steps of: further formingsaid fabric body coated with said polymeric material into a selectedshape subsequent to curing of said thermoset material by; providing amold having a cavity of said selected shape; placing said fabric bodyinto said cavity; inserting a balloon into said fabric body; forcefullyinflating said balloon while heating said cavity to require said fabricbody to take the shape of said cavity; and cooling said shaped fabricbody to cause the latter to retain said selected shape.
 46. A method ofproviding for assistance to a selected heart chamber of a livingorganism having a blood circulatory system, said method comprising thesteps of: providing an artificial flow path for a flow of blood leadingfrom said circulatory system and returning to said circulatory systemdownstream of said selected heart chamber; providing a variable-volumechamber in said artificial flow path; providing a pair of like-disposedone-way valves bracketing said variable-volume chamber in saidartificial flow path; providing means securing said pair of one-wayvalves in respective ones of a pair of portions of said artificial flowpath; expanding and contracting said variable-volume chamber to withdrawblood from said circulatory system, and to return said blood to saidcirculatory system downstream of said selected heart chamber to assistor replace the function of the heart chamber in circulating said bloodin said circulatory system; using a singular flexible wall member todefine said variable-volume chamber; using a pair of respectiveartificial conduit members to define said pair of portions of saidartificial flow path and to receive said one-way valves; and sealinglycontacting said pair of respective artificial conduit members directlywith said singular flexible wall member; whereby blood from saidcirculatory system in flowing past said pair of one-way valves andthrough said variable-volume chamber contacts only said singularflexible wall member, said pair of artificial conduit members, said pairof one-way valves, and said means securing said pair of one-way valvesinto said pair of artificial conduit members.
 47. A conduit for carryingblood comprising: a tubular body having an inner surface bounding a flowpath for said blood; prosthetic valve means sealingly disposed in saidflow path for limiting blood flow therein to a single direction, andincluding at least one valve leaflet; said flexible conduit memberfurther defining the same number of sinuses as the number of valveleaflets of said prosthetic valve, each said sinus being downstream ofand axially aligning respectively with a respective one leaflet of saidprosthetic valve; wherein each said sinus of said flexible conduit isshallower and longer than a human natural aortic valve sinus.
 48. Theconduit of claim 47 wherein said sinus has an aspect ratio of at least1.3.
 49. The conduit of claim 48 wherein said sinus has an aspect ratioin the range from about 1.3 to about 1.6 or more.
 50. The conduit ofclaim 49 wherein said sinus has an aspect ratio of substantially 1.45.51. The conduit of claim 47 wherein said prosthetic valve is a porcinexenograft.
 52. The conduit of claim 47 further including a stentingstructure for supporting said prosthetic valve means, said stentingstructure being disposed outside of said tubular body and being isolatedthereby from contact with blood flowing in said conduit.
 53. The conduitof claim 47 wherein each said sinus at a downstream termination thereofrejoins a cylindrical projection of said tubular body at an acuteglancing angle.
 54. A valved prosthetic conduit for carrying aunidirectional blood flow in a living organism, said valved conduitcomprising: a prosthetic valve; a prosthetic conduit in which said valveis secured; a stenting structure for said prosthetic valve, saidstenting structure being disposed outside of said conduit; whereby thestenting structure is isolated from contact with flowing blood by saidconduit.
 55. The valved conduit of claim 54 wherein said conduit isimpervious to blood and defines a porous inner surface providing for astable biological interface within said conduit.
 56. The valved conduitof claim 54 wherein said conduit is formed of flexible andshape-retaining fabric defining plural sinuses downstream of saidprosthetic valve, said prosthetic valve including plural valve leafletsand said plural sinuses being the same in number and aligning axiallywith the valve leaflets of said prosthetic valve.
 57. A blood-carryingconduit apparatus,comprising: a first flexible conduit member defining aflow path for communicating a flow of blood therethrough, and having aflexible side wall defining a blood-contacting inner surface boundingsaid flow path; a second blood-carrying member defining a flow path forcommunicating blood therein; said side wall including a reentrantportion defining an end surface for said first flexible conduit member;and means urging said end surface of said conduit member sealingly intoengagement with said second blood-carrying member.
 58. The conduitapparatus of claim 57 wherein said means for urging further includingmeans for resiliently accommodating relative axial movement of saidconduit member relative to said second member while maintaining sealingcontact therebetween.
 59. The conduit apparatus of claim 58 wherein saidmeans urging said end surface of said conduit into sealing engagementwith said second member includes a collar member circumscribing saidconduit member and engaging said second member and a radially extendingportion of said conduit member to urge the latter into sealingengagement at said end surface with said second member.
 60. The conduitapparatus of claim 59 wherein said means for resiliently accommodatingrelative axial movement of said conduit member relative to said secondmember includes an axially-resilient element interposing between saidcollar member and said radially extending portion of said conduitmember.
 61. The conduit apparatus of claim 60 wherein saidaxially-resilient element includes a circumferentially extending wavewasher interposing between said collar and said radially extendingportion of said conduit.